This study tested the hypothesis that the use of corporal punishment (CP), such as slapping a child's hand or “spanking,” is associated with restricted development of cognitive ability. Cognitive ability was measured at the start of the study and 4 years later for 806 children age 2-4 and 704 children age 5-9 in the National Longitudinal Study of Youth. The analyses controlled for 10 parenting and demographic variables. Children of mothers in both cohorts who used little or no CP at Time 1 gained cognitive ability faster than children who were not spanked. The more CP experienced, the more they fell behind children who were not spanked.